Method and apparatus for transmitting and receiving high speed data using code division multiple access channels

ABSTRACT

The present invention describes a spread spectrum communication system wherein the frequency of carriers and the code channels of the carriers or both for transmission to a given remote station user vary in time. This provides for a direct sequence spectrum communications system which changes frequency or code channel according to a predetermined pattern. The code channels and frequencies can be determined in accordance with a deterministic function or based upon a subset of the data to be transmitted. A receiver structure is also described for receiving the same.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present application for patent is a Divisional application ofapplication Ser. No. 11/401,971 filed Apr. 10, 2006, which is aContinuation of application Ser. No. 09/113,770 entitled, “Method andApparatus for Transmitting and Receiving High Speed Data Using CodeDivision Multiple Access Channels” filed Jul. 10, 1998, now allowed, andassigned to the assignee hereof and hereby expressly incorporated byreference herein.

BACKGROUND

1. Field

The present invention relates to communications. More particularly, thepresent invention relates to a novel and improved communication systemwherein the user transmits data using code division multiple accesscommunication channels which are transmitted in varying frequency bandsand varying code channels.

2. Background

The present invention is concerned with transmitting data at rates whichare higher than the capacity of a single code division multiple access(CDMA) channel.

Many solutions to this problem have been proposed. One such solution isto allocate multiple CDMA code channels to the users and allow thoseusers to transmit data in parallel on the plurality of code channelsavailable to them. Two methods for providing multiple CDMA channels foruse by a single user are described in copending U.S. patent applicationSer. No. 08/431,180, entitled “METHOD AND APPARATUS FOR PROVIDINGVARIABLE RATE DATA IN A COMMUNICATIONS SYSTEM USING STATISTICALMULTIPLEXING”, filed Apr. 28, 1997 and U.S. Pat. No. 5,777,990 entitled“METHOD AND APPARATUS FOR PROVIDING VARIABLE RATE DATA IN ACOMMUNICATIONS SYSTEM USING NON-ORTHOGONAL OVERFLOW CHANNELS”, issuedJul. 7, 1998, both of which are assigned to the assignee of the presentinvention and are incorporated by reference herein. In addition,frequency diversity can be obtained by transmitting data over multiplespread spectrum channels that are separated from one another infrequency. A method and apparatus for redundantly transmitting data overmultiple CDMA channels is described in U.S. Pat. No. 5,166,951, entitled“HIGH CAPACITY SPREAD SPECTRUM CHANNEL”, which is incorporated byreference herein.

CDMA modulation provides one means for establishing communicationbetween users in a large system which includes a number of such users.Other techniques, such as time division multiple access (TDMA),frequency division multiple access (FDMA) and AM modulation schemes(such as amplitude companded single sideband (ACSSB)) are known in theart. However, the spread spectrum modulation technique of CDMA hassignificant advantages over these modulation techniques for multipleaccess communication systems. The use of CDMA techniques in a multipleaccess communication system is disclosed in U.S. Pat. No. 4,901,307,entitled “SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USINGSATELLITE OR TERRESTRIAL REPEATERS”, assigned to the assignee of thepresent invention and incorporated by reference herein. The use of CDMAtechniques in a multiple access communication system is furtherdisclosed in U.S. Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FORGENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM”,assigned to the assignee of the present invention and incorporated byreference herein.

CDMA by its inherent nature of being a wideband signal offers a form offrequency diversity by spreading the signal energy over a widebandwidth. Therefore, frequency selective fading affects only a smallpart of the CDMA signal bandwidth. Space or path diversity is obtainedby providing multiple signal paths through simultaneous links from amobile user through two or more cell-sites. Furthermore, path diversitymay be obtained by exploiting the multipath environment through spreadspectrum processing by allowing a signal arriving with differentpropagation delays to be received and processed separately. Examples ofthe utilization of path diversity are illustrated in copending U.S. Pat.No. 5,101,501 entitled “SOFT HANDOFF IN A CDMA CELLULAR TELEPHONESYSTEM”, and U.S. Pat. No. 5,109,390 entitled “DIVERSITY RECEIVER IN ACDMA CELLULAR TELEPHONE SYSTEM”, both assigned to the assignee of thepresent invention and incorporated by reference herein.

SUMMARY OF THE INVENTION

In a first embodiment of a transmitter in accordance with the presentinvention, data is encoded, spread and provided to a bank ofupconverters, each associated with a unique local oscillator. Eachupconverter upconverts the spread data to a different center frequency.A switch selects one of the upconverted signals in accordance with adeterministic pseudorandom sequence. Alternatively, the spread data isprovided to an upconverter which is driven by a variable frequencysynthesizer which generates a signal having a frequency determined inaccordance with a deterministic pseudorandom sequence.

Three embodiments of a receiver are presented for receiving the datatransmitted by the first transmitter embodiment. In a first receiverembodiment, the received data is passed to a bank of down convertersdriven by local oscillators, each of which is tuned to a differentfrequency. The downconverted data is provided to a switch which selectsone of the downconverted data streams in accordance with a delayedversion of the deterministic sequence used to select the upconversionfrequency. In a second receiver embodiment, the received data isprovided to a downconverter that downconverts the signal using theoutput of a variable frequency synthesizer which selects its outputfrequency in accordance with a delayed version of the deterministicsequence used to select the upconversion frequency. In a third receiverembodiment, the received data is provided to a bank of down converters,each of which downconverts the signal in accordance with a differentcenter frequency. The downconverted signals are, then, despread anddecoded. A control processor then selects which of the received signalsto output based on values (commonly referred to as “quality metrics”)calculated to determine the quality of a received frame of data, suchas: (1) the results of a cyclic redundancy check, (2) the symbol errorrate, and (3) trellis metrics, such as the Yamamoto metric.

In a second embodiment of the transmitter of the present invention, asubset of the information bits to be transmitted are used to select thecenter frequency of the spread spectrum signal. In one embodiment, thedata is packetized, encoded and spread. The spread data is provided to abank of upconverters, each of which upconvert the spread data to adifferent center frequency. An upconverted stream of data is thenselected from among the streams of data output from the bank ofupconverters, based upon a subset of the upconverted stream of data tobe transmitted. Alternatively, the data is packetized, encoded, spreadand provided to an upconverter that upconverts the data in accordancewith a signal generated by a variable frequency synthesizer that selectsits output frequency based on a subset of the information bits to betransmitted.

At the receiver, the received data is provided to a bank of downconverters each of which downconverts the signal in accordance with adifferent center frequency.

The down converted signals are despread and decoded. A control processorthen selects which of the received signals to output based on framequality metrics, such as: (1) the results of a cyclic redundancy check,(2) the symbol error rate, and (3) trellis metrics, such as the Yamamotometric. The decoded data, as well as a data corresponding to thefrequency on which the data was received, is demultiplexed into anoutput data stream.

In a third embodiment of the transmitter of the present invention, eachtransmitter is given a plurality of code channels upon which it cantransmit data. The transmitter selects the code channel upon which totransmit the data in accordance with a subset of the information data tobe transmitted. At the receiver, the received data is provided to a bankof code channel dechannelizers. Each of the despread signals is providedto a decoder. The decoded data is provided to a control processor whichselects data to output and demultiplexes that data with the bitscorresponding to the code channel upon which the data was received.

In the fourth embodiment of the present invention, a subset of theinformation bits to be transmitted is used to select both theupconversion frequency of the spread spectrum signal and the codechannel upon which the signal is to be transmitted. At the receiver, thereceived data is provided to a bank of downconverters, each of whichdownconverts the signal in accordance with a different center frequency.Each of the down converted signals is in turn provided to a bank of codechannel dechannelizers. Each of the despread signals is provided to adecoder. The decoded data is provided to a control processor whichselects the decoded data to output and demultiplexes that data with thedata corresponding to the code channel upon which the data was receivedand to the frequency channel upon which the data was received.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 is a diagram illustrating an one embodiment of the presentinvention in which the CDMA channel is frequency hopped based on adeterministic signal using a bank of down converters;

FIG. 2 a is a diagram illustrating one embodiment of the presentinvention in which the CDMA channel is frequency hopped based on adeterministic signal using a variable frequency synthesizer;

FIG. 2 b is a simplified block diagram of a DDS in accordance with oneembodiment of the present invention;

FIG. 3 is a diagram illustrating a receiver system in accordance withone embodiment of the present invention which is capable of receivingdata transmitted on CDMA channels with center frequencies selected basedon a deterministic selection using a bank of local oscillators;

FIG. 4 is diagram illustrating a receiver system in accordance with analternative embodiment of the present invention which is capable ofreceiving data transmitted on CDMA channels with center frequenciesselected based on a deterministic selection using variable frequencysynthesizer;

FIG. 5 is diagram illustrating a receiver system in accordance withanother alternative embodiment which is capable of receiving datatransmitted on CDMA channels with center frequencies selected based on adeterministic selection wherein the signal is down converted at eachpossible center frequency and then one is selected based on the qualitymetrics of the frame;

FIG. 6 is a diagram illustrating an embodiment wherein the CDMA channelis frequency hopped based on a subset of the information bits to betransmitted using a bank of up converters;

FIG. 6A is a diagram illustrating an embodiment wherein the CDMA channelis frequency hopped based on a scrambled subset of the information bitsto be transmitted using a bank of up converters;

FIG. 7 is a diagram illustrating an exemplary implementation of thesecond embodiment wherein the CDMA channel is frequency hopped based ona subset of the information bits to be transmitted using a variablefrequency synthesizer;

FIG. 8 is a diagram illustrating an exemplary implementation of thethird embodiment wherein the CDMA code channel is selected based on asubset of the information bits to be transmitted using a bank of codechannel channelizers;

FIG. 9 is a diagram illustrating an exemplary implementation of thethird embodiment wherein the CDMA code channel is selected based on asubset of the information bits to be transmitted using a code symbolgenerator;

FIG. 10 is diagram illustrating the third implementation of a receiversystem capable of receiving data transmitted on a plurality of CDMA codechannels wherein the signal is despread with each possible code sequenceand then one is selected based on the quality metrics of the frame;

FIG. 11 is a diagram illustrating an exemplary implementation of thethird embodiment wherein the CDMA code channel and the center frequencyare selected based on a subset of the information bits to be transmittedusing a code symbol generator; and

FIG. 12 is diagram illustrating the third implementation of a receiversystem capable of receiving data transmitted on a plurality of CDMA codechannels and frequencies wherein the signal is despread with eachpossible code sequence and down converted with each possible frequencyand then one is selected based on the quality metrics of the frame.

DETAILED DESCRIPTION

FIG. 1 illustrates the first embodiment of the present invention,wherein the CDMA channels change frequency in accordance with adeterministic signal. The information data to be transmitted is providedto Cyclic Redundancy Check (CRC) generator 2. CRC generator 2 generatesand appends a set of bits that can be used to check the correctness ofthe decoded data at the receiver. The information data, together withthe appended set of bits from CRC generator 2, is provided to encoder 4.In one embodiment, encoder 4 is a convolutional encoder, though thepresent invention is equally applicable to any error correction encoder.Convolutional encoders are well known in the art. In one embodiment, theconvolutional encoder also includes an interleaver. Interleavers arealso well known in the art.

The encoded symbols are then provided to channelizer 6 which spreads theencoded symbols in accordance with a spreading sequence provided bysequence generator 8. In the one embodiment, sequence generator 8 is aWalsh symbol generator that provides sequences of symbols in accordancewith orthogonal Walsh sequences. This is used to separate the channelsin a CDMA system. The Walsh sequence data is provided to scramblingmeans 10 which scrambles the data in accordance with a pseudorandomsequence provided by PN generator 12. Channelizers and sequencegenerators are well known in the art and are described in detail in theaforementioned U.S. Pat. No. 5,103,459. It should be noted that manyother combinations of channelizer and scrambler are also possible aslong as the result is to channelize the various users. The embodimentshown distinguishes channels from one another by orthogonal Walshencoding followed by a scrambler. However, other orthogonal sequencescan also be used to provide channelization. Furthermore, thechannelization does not have to be performed by a set of orthogonalsequences. For example, a single stage channelizer where each user isassigned a different PN code could be used.

The scrambled data is provided to a bank of mixers 14 a-14 n. Each mixeris driven by a corresponding local oscillator 16 a-16 n. The upconverteddata from each of mixers 14 a-14 n is provided to switch 18. In thepreferred embodiment, the local oscillator frequencies are equallyseparated in frequency, so that the frequency of the n^(th) LO isf₀+NΔ_(lo). In the preferred embodiment, the local oscillatorfrequencies are separated by the chip rate of the PN generator or bysome multiple thereof so that Δ_(lo) is the chip rate or some multipleof the chip rate. Switch 18 selects which one of the upconverted signalsis to provide to coupled to transmitter (TMTR) 20. The upconvertedsignal that is provided to transmitter 20 is selected in accordance witha signal provided by control processor 22. In the illustratedembodiment, control processor 22 generates the selection signal based ona pseudorandom process. The pseudorandom process can be generated usingany one of many methods which are well known in the art for generatingsuch sequences. For example, the pseudorandom sequence can be generatedby a linear or non-linear feedback shift register. It may also begenerated by a cryptographic keystream generator. Any of thesetechniques can use an identity of the mobile station, such as theelectronic serial number (ESN), a public key, or a secret key. Thesetechniques are well known in the art. In an alternative embodiment, theselection signal can be a sequential selection of the first, then secondup to the n-th upconverted signal. In another alternative embodiment,the selected frequency may be based upon channel conditions. Thereceiving system may measure the performance of each channel and thenfeed the preferred frequency back to the transmitter for use. This maybe done by monitoring a signal which is continuously transmitted, suchas a pilot. The selected signal is provided to transmitter 20 whichfilters and amplifies the signal and provides it for transmissionthrough antenna 24. It should be understood that in the preferredembodiment of the present invention, at least one other signal similarlygenerated will be multiplexed together. Preferably, the number of suchsimilarly generated signals will be equal to the number of mixer 14 andlocal oscillator 16 combinations. For example, in the case of theembodiment illustrated in FIG. 1, three such signals will be multiplexedand transmitted through transmitter 20. Accordingly, data from threedifferent sources (and coupled to the transmitter from three differentswitches 18, only one of which is shown) will be multiplexed togetherbefore transmission by the transmitter 20. Each switch 18 selects amixer 14 that is coupled to a local oscillator 16 that is operating at adifferent frequency from the frequency of each of the other localoscillators 16 generating the signals that are being concurrentlyselected by each other switch 18.

FIG. 2 a illustrates an alternative implementation of the firstembodiment wherein the bank of upconverters is replaced with a variablefrequency synthesizer. The information data to be transmitted isprovided to Cyclic Redundancy Check (CRC) generator 50. CRC generator 50generates and appends a set of bits that can be used to check thecorrectness of the decoded data at the receiver. The bits from CRCgenerator 50 are provided to encoder 52. In one embodiment, encoder 52is a convolutional encoder.

The encoded symbols are then provided to channelizer 54 whichchannelizes the encoded symbols in accordance with a code sequenceprovided by sequence generator 56. In one embodiment, sequence generator56 is a Walsh symbol generator that provides sequences of code symbolsin accordance with orthogonal Walsh sequences. The Walsh sequence datais provided to scrambling means 58 which scrambles the data inaccordance with a pseudorandom sequence provided by PN generator 60.Channelizers and sequence generators are well known in the art and aredescribed in detail in the aforementioned U.S. Pat. No. 5,103,459.

The scrambled data is provided to mixer 62. Mixer 62 is driven byvariable frequency synthesizer 64. Variable frequency synthesizer 64outputs a driving frequency to mixer 62 in accordance with a signalprovided by control processor 70. In one embodiment, control processor70 generates the frequency selection signal based on a pseudorandomprocess. In an alternative embodiment, the selection signal can be asequential selection of the first, then second up to the n-thupconverted signal. The upconverted signal is provided to transmitter 66which filters and amplifies the signal and provides it for transmissionthrough antenna 68. Accordingly, in an embodiment in which the frequencysynthesizer 64 generates three frequencies, a signal generated will havea first frequency for a first period of time, a second frequency for asecond period of time, and a third frequency for a third period of time.This sequence will repeat, such that the frequency of the signalgenerated will alternate between the three frequencies over time.

In one embodiment of the present invention, in order to ease the burdenon the receiver, a phase relationship is maintained between the signalgenerated by the variable frequency synthesizer having a first frequencyat a first period in time and the signal generated by the variablefrequency synthesizer having that first frequency, but at each latertime.

In accordance with one embodiment of the present invention, therelationship between the phase of the signal over time is established byusing a direct digital synthesizer (DDS) as follows. FIG. 2 b is asimplified block diagram of a DDS in accordance with one embodiment ofthe present invention. The DDS shown in FIG. 2 b comprises summingcircuit 201, phase register 203, look-up table 205, and analog todigital converter (A/D) 207. A phase increment signal is applied to afirst input to summing circuit 201. The output from the phase register203 is applied to a second input to the summing circuit 201. The outputfrom the summing circuit is stored in the phase register 203. A registerclock is applied to the phase register to shift the value at the inputof the register 203 to the output. Therefore, after each cycle of theregister clock, the output from the summing circuit is incremented bythe value of the phase increment. The output from phase register 203 isapplied to look-up table 205. Look-up table 205 converts the valueoutput from phase register 203 from a number representing the relativephase of the output signal to a value that represents the amplitude of asinusoidal signal at that point in the cycle that corresponds with thephase value. It should be clear that the faster the register clock runs,the higher the frequency of the output signal. Likewise, the larger thephase increments, the higher the frequency.

Therefore, either the phase increment or the register clock can be usedto determine the frequency that will be generated. The A/D converter 207converts the value output from look-up table 207 into a correspondinganalog voltage level.

In accordance with the present invention, memory device 209 is coupledto the output from phase register 203. Prior to the synthesizer changingfrequencies, the value of the phase register 203 is stored in memory209. When the frequency is again generated at a later time, the valuestored in memory 209 is coupled to offset processor 211. Offsetprocessor 211 adjusts the value to account for the amount of time thathas elapsed since that frequency was last generated. That is, in oneembodiment, offset processor 211 determines the number of cycles of thephase clock that would have occurred during the period that has elapsedfrom the time that frequency was last generated. This number ismultiplied by the value of the phase increment. The product of thismultiplication is added to the value stored in memory 209. The resultingsum is then restored into the phase register 203.

FIG. 3 illustrates a first implementation of a receiver designed toreceive spread spectrum data which changes frequency in accordance withthe transmission systems of FIGS. 1 and 2. Referring to FIG. 3, thetransmitted signal is received by antenna 100 and provided to receiver(RCVR) 102. Receiver 102 filters and amplifies the signal and providesthe received signal to a bank of down converters 104 a-104 n. Eachdownconverter 104 a-104 n is driven by a corresponding local oscillator106 a-106 n. Switch 108 selects the signal to provide to dechannelizer110 in accordance with a selection signal provided by control processor114 which is a time delayed version of selection signal provided bycontrol processors 22 and 70.

The down converted signals are provided to switch 108. Switch 108selectively provides one of the down converted signals to descrambler110. Descrambler 110 unscrambles the downconverted signal in accordancewith a pseudorandom sequence provided by PN generator 112. Thedescrambled sequence is provided to dechannelizer 116 whichdechannelizes the signal in accordance with sequence provided bysequence generator 118. In one embodiment, sequence generator 118 is anorthogonal Walsh sequence generator. Data is provided to decoder 120which decodes the data based on the type of encoder used by thetransmission system. In one embodiment, the encoder is a convolutionalencoder and decoder 120 is a trellis decoder. The decoded data isprovided to CRC check element 122 which tests to determine whether thedecoded check bits correspond to the decoded information bits. If theydo, then the data is provided to the user, otherwise an erasure isdeclared.

FIG. 4 illustrates a second embodiment of a receiver designed to receivespread spectrum data which is changes frequency in accordance with thetransmission systems of FIGS. 1 and 2. Referring to FIG. 4, thetransmitted signal is received by antenna 150 and provided to receiver(RCVR) 152. Receiver 152 filters and amplifies the signal and providesthe received signal to down converter 154. Downconverter 154 is drivenby variable frequency synthesizer 156. Variable frequency synthesizer156 outputs a frequency in accordance with a selection signal providedby control processor 164. In accordance with one embodiment of thepresent invention, variable frequency synthesizer 156 is a DDS similarto the DDS that is shown in FIG. 2 b. The DDS performs the same storeand restore function that was described above with respect to thetransmitter in order to ensure that the transmit and receive signalswill remain in phase synchronization. That is, the value that is held inphase register 203 is stored in memory 209 each time the frequency isabout to change. The value of stored in memory 209 is then offset andrestored into phase register 203 when the frequency of the DDS returnsto that frequency. In this way, the receiver remains synchronized to thetransmitter as the frequency alternates between the differentfrequencies that are to be generated by the DDS.

The downconverted signal is provided to descrambler 160. Descrambler 160unscrambles the downconverted signal in accordance with a pseudorandomsequence provided by PN generator 162. The descrambled sequence isprovided to dechannelizer 166 which dechannelizes the signal inaccordance with the sequence provided by sequence generator 168. In oneembodiment, sequence generator 168 is an orthogonal Walsh sequencegenerator. The data output from dechannelizer 166 is provided to decoder170 which decodes the data based on the type of encoder used by thetransmission system. In one embodiment, the encoder is a convolutionalencoder and decoder 170 is a trellis decoder. The decoded data isprovided to CRC check element 172 which tests to determine whether thedecoded check bits correspond to the decoded information bits. If theydo the data is provided to the user, otherwise an erasure is declared.

FIG. 5 illustrates a third embodiment of a receiver designed to receivespread spectrum data which changes frequency in accordance with thetransmission systems of FIGS. 1 and 2. Referring to FIG. 5, thetransmitted signal is received by antenna 200 and provided to receiver(RCVR) 202. Receiver 202 filters and amplifies the signal and providesthe received signal to a bank of downconverters 204 a-204 n. Eachdownconverter 204 a-204 n is driven by a corresponding local oscillator206 a-206 n.

Each downconverted signal is provided to a corresponding descrambler 210a-210 n. Descramblers 210 a-210 n unscramble the down-converted signalin accordance with a pseudorandom sequence provided by a correspondingPN generator 212 a-212 n. The descrambled sequences are provided todechannelizers 216 a-216 n which dechannelizes the signal in accordancewith sequence provided by a corresponding sequence generator 218 a-218n. In one embodiment, sequence generators 218 a-218 n are orthogonalWalsh sequence generators. The despread data is provided to decoders 220a-220 n which decode the data based on the type of encoder used by thetransmission system. In one embodiment, the encoder is a convolutionalencoder and decoders 220 a-220 n are trellis decoders. The decoded datais provided to CRC check element 222 a which determines whether thedecoded check bits correspond to the decoded information bits.

A set of values (commonly referred to as “quality metrics”), calculatedto determine the quality of a received frame of data, is provided tocontrol processor 224 for each decoded stream of data. Control processor224 outputs to the user the frame having the best quality as determinedby the values of the quality metrics. If all of the decoded frames areof inadequate quality as determined by the values of the qualitymetrics, then an erasure is declared. Examples of quality metrics whichcan be used by control processor 224 to select the frame include: (1)accumulated branch metrics from trellis decoders 220, (2) symbol errorrate (SER), and (3) CRC check results.

FIG. 6 illustrates an alternative embodiment of the present invention,wherein the CDMA channels change frequency in accordance with a subsetof the information bits to be transmitted. The information data to betransmitted is provided to multiplexer (MUX) 250, which provides asubset of bits for selecting the center frequency on a first output andthe remaining bits to be transmitted to a second output. In oneembodiment, the information bits are used to select the frequency fortransmission. However, the packetized bits from CRC generator 252 or theencoded symbols from convolutional encoder 254 can be used to select theupconversion frequency. The subset of information bits used to selectthe upconversion frequency are provided to control processor 266. Inaccordance with the subset of information bits, control processor 266generates a command signal to switch 264. In order to providerandomization of the transmitted frequency, a preferred embodiment wouldscramble the subset of information bits provided to control processor266. Such scrambling provides makes the transmitted frequency random. Ina preferred embodiment, a subset of the bits from PN generator 262 isused to scramble the bits supplied to control processor 266 as shown inFIG. 6A.

The remaining information bits to be transmitted are provided to CRCgenerator 252, which generates and appends a set of bits that can beused to check whether the decoded data was received correctly at thereceiver. The bits from CRC generator 252 are provided to encoder 254.In one embodiment, encoder 254 is a convolutional encoder, though thepresent invention is equally applicable to any error correction encoder.Convolutional encoders are well known in the art.

The encoded symbols are then provided to channelizer 256 whichchannelizes the encoded symbols in accordance with a sequence providedby sequence generator 258. In one embodiment, sequence generator 258 isa Walsh symbol generator that provides sequences of symbols inaccordance with orthogonal Walsh sequences. The Walsh sequence data isprovided to scrambling means 260 which scrambles the data in accordancewith a pseudorandom sequence provided by PN generator 262. Suchchannelizers and sequence generators are well known in the art and aredescribed in detail in the aforementioned U.S. Pat. No. 5,103,459.

The scrambled data is provided to a bank of mixers 268 a-268 n. Eachmixer 268 a-268 n is driven by a corresponding local oscillator 270a-270 n. The upconverted data from each mixer 268 a-268 n is provided toswitch 264. Switch 264 selects one of the upconverted signals to provideto transmitter (TMTR) 274. The upconverted signal that is provided totransmitter 274 is selected in accordance with the selection signalprovided by control processor 266.

FIG. 7 illustrates an alternative implementation of the secondembodiment of the present invention wherein the CDMA channels arefrequency hopped in accordance with a subset of the information bits tobe transmitted. The information data to be transmitted is provided tomultiplexer (MUX) 300, which provides the a subset of bits for selectingthe center frequency on a first output and the remaining bits to betransmitted to a second output. In one embodiment, the information bitsare used to select the frequency for transmission. However, thepacketized bits from CRC generator 302 or the encoded symbols fromconvolutional encoder 304 can be used to select the upconversionfrequency. The subset of information bits used to select theupconversion frequency are provided to control processor 316. Inaccordance with the subset of information bits, control processor 316generates and provides a signal to variable frequency synthesizer 320.In accordance with one embodiment of the present invention, thesynthesizer 320 is a DDS having a memory for storing phase values whenthe frequency changes, as described above and illustrated in FIG. 2 b.

The remaining information bits to be transmitted are provided to CyclicRedundancy Check (CRC) generator 302. CRC generator 302 generates andappends a set of bits that can be used to check the correctness of thedecoded data at the receiver. The bits from CRC generator 302 areprovided to encoder 304. In one embodiment, encoder 304 is aconvolutional encoder.

The encoded symbols are then provided to channelizer 306 whichchannelizes the encoded symbols in accordance with a sequence providedby sequence generator 308. In one embodiment, sequence generator 308 isa Walsh symbol generator that provides sequences of symbols inaccordance with orthogonal Walsh sequences. The Walsh sequence data isprovided to scrambling means 310 which scrambles the data in accordancewith a pseudorandom sequence provided by PN generator 312. Channelizersand sequence generators are well known in the art and are described indetail in the aforementioned U.S. Pat. No. 5,103,459.

The scrambled data is provided to mixer 318. Mixer 318 is driven byvariable frequency synthesizer 320. Variable frequency synthesizer 320outputs a driving frequency to mixer 318 in accordance with a signalprovided by control processor 316. In one embodiment, control processor316 generates the frequency selection signal based on a subset of theinformation bits. The upconverted signal is provided to transmitter 324which filters and amplifies the signal and provides it for transmissionthrough antenna 326.

FIG. 8 illustrates an embodiment of the present invention wherein theCDMA channels change code channels in accordance with a subset of theinformation bits to be transmitted. It should be noted that theembodiment illustrated in FIG. 8 is equally applicable to the casewherein the code channel is selected in accordance with a pseudorandomfunction analogous to embodiments of the present invention such as thoseillustrated in FIGS. 1 and 2, wherein the frequency is selected based ona pseudorandom code.

The information data to be transmitted is provided to multiplexer (MUX)350, which provides a subset of bits for selecting the code channel on afirst output and the remaining bits to be transmitted to a secondoutput. In one embodiment, the information bits are used to select thecode channel for transmission. However, the packetized bits from CRCgenerator 352 or the encoded symbols from convolutional encoder 354 canbe used to select the code channel. The subset of information bits usedto select the code channel are provided to control processor 366. Inaccordance with the subset of information bits, control processor 366generates and provides a code channel selection signal to switch 364.

The remaining information bits to be transmitted are provided to CRCgenerator 352, which generates and appends a set of bits that can beused to check whether the decoded data was correctly received at thereceiver. The bits from CRC generator 352 are provided to encoder 354.In one embodiment, encoder 354 is a convolutional encoder, though thepresent invention is equally applicable to any error correction encoder.The implementation of convolutional encoders is well known in the art.

The encoded symbols are then provided to a bank of code channelchannelizers 356 a-356 n. Each code channel channelizer is provided witha unique sequence from a corresponding sequence generator 358 a-358 n.In one embodiment, sequence generators 358 a-358 n are Walsh symbolgenerators that provides sequences of symbols in accordance withorthogonal Walsh sequences. The Walsh sequence data from eachchannelizer 356 a-356 n is provided to switch 364. Switch 364selectively provides one of the spread data sequences to scramblingmeans 360. Switch 364 selects which data sequence to provide at itsoutput based on a selection signal from control processor 366. Thecontrol processor 366 generates the signal in accordance with a subsetof information bits from control processor 366.

Scrambling means 360 scrambles the data in accordance with apseudorandom sequence provided by PN generator 362. Channelizers andsequence generators are well known in the art and are described indetail in the aforementioned U.S. Pat. No. 5,103,459. The scrambled datais provided to mixer 368. Mixer 368 is driven by a corresponding localoscillator 370. The upconverted data is provided to transmitter (TMTR)374.

FIG. 9 illustrates an alternative embodiment of the present invention,wherein the CDMA channels change code channel in accordance with asubset of the information bits to be transmitted. It should be notedthat the embodiment illustrated in FIG. 9 is equally applicable to thecase in which the code channel is selected in accordance with apseudorandom function analogous to the embodiment of the presentinvention illustrated in FIGS. 1 and 2 in which the frequency isselected based on a pseudorandom code.

The information data to be transmitted is provided to multiplexer (MUX)400, which provides a subset of bits for selecting the code channel on afirst output and the remaining bits to be transmitted to a secondoutput. In one embodiment, the information bits are used to select thecode channel for transmission. However, the packetized bits from CRCgenerator 402 or the encoded symbols from convolutional encoder 404 canbe used to select the code channel. The subset of information bits usedto select the code channel is provided to control 416. In accordancewith the subset of information bits, control processor 416 generates andprovides a code channel selection signal to Walsh symbol generator 414.

The remaining information bits to be transmitted are provided to CRCgenerator 402, which generates and appends a set of bits that can beused to check the correctness of the decoded data at the receiver. Thebits from CRC generator 402 are provided to encoder 404. In oneembodiment, encoder 404 is a convolutional encoder, though the presentinvention is equally applicable to any error correction encoder. Theimplementation of convolutional encoders is well known in the art.

The encoded symbols are then provided to channelizer 406. Channelizer406 is provided with a time varying spreading sequence fromcorresponding variable sequence generator 414. In one embodiment,variable sequence generators 414 provides sequences in accordance with apredetermined set of orthogonal Walsh sequences. The Walsh sequence datafrom channelizers 406 is provided to scrambler 408 which scrambles thedata in accordance with a pseudorandom sequence provided by PN generator410. As noted above, such channelizers and sequence generators are wellknown in the art and described in detail in the aforementioned U.S. Pat.No. 5,103,459. The scrambled data is provided to mixer 418. Mixer 418 isdriven by a corresponding local oscillator 420. The upconverted data isprovided to transmitter (TMTR) 374 for transmission through antenna 426.

FIG. 10 illustrates a receiver for receiving a signal in accordance withthe present invention, wherein the CDMA channels change code channel inaccordance with a subset of the information bits to be transmitted. Thesignal is demodulated in accordance with all possible code channelsequences and the received signal is selected from all of thedemodulated signals through an analysis of values (commonly referred toas “metrics”) calculated to determine the quality of the receivedsignal. The transmitted signal is received by antenna 450 and providedto receiver (RCVR) 452. Receiver 452 filters and amplifies the signaland provides the received signal to downconverter 454. Downconverters454 is driven by local oscillator 456.

The downconverted signal is provided to a descrambler 458. Descrambler458 unscrambles the down-converted signal in accordance with apseudorandom sequence provided by a corresponding PN generator 460. Thedescrambled sequences are provided to the bank of dechannelizers 462a-462 n which dechannelizes the signal in accordance with sequenceprovided by a corresponding sequence generator 464 a-464 n. In oneembodiment, sequence generators 464 a-464 n are an orthogonal Walshsequence generators. The data is provided to decoders 466 a-466 n whichdecodes the data based on the type of encoder used by the transmissionsystem. In one embodiment, the encoder is a convolutional encoder anddecoders 466 a-466 n are trellis decoders. The decoded data is providedto CRC check elements 468 a-468 n which determine whether the decodedcheck bits correspond to the decoded information bits.

For each decoded stream of data and a set of quality metrics is providedto control processor 470. Control processor 470 selects for output tothe user, the frame with the best quality based on the values of the setof quality metrics. If all of the decoded frames have inadequate qualityas determined by the values of the metrics, then an erasure is declared.Examples of quality metrics which can be used by control processor 470to select the frame, include: (1) accumulated branch metrics fromtrellis decoders 466 a-466 n, (2) symbol error rate (SER), and (3) CRCcheck results.

FIG. 11 illustrates the another embodiment of the transmission system ofthe present invention wherein both the modulation sequence andupconversion frequency is selected in accordance with a subset of theinformation bits to be transmitted. It should be noted that theembodiment illustrated in FIG. 11 is equally applicable to the casewherein the code channel and frequency of upconversion are selected inaccordance with a deterministic function. This can be done byprogramming control processor 522.

The information data to be transmitted is provided to multiplexer (MUX)500, which provides a subset of bits for selecting the code channel andthe frequency of upconversion and the remaining bits to be transmittedon a third output. In alternative embodiments, the packetized bits fromCRC generator 502 or the encoded symbols from convolutional encoder 504can be used to select the code channel and the frequency of theupconversion. The subset of information bits used to select the codechannel and the frequency of the upconversion are provided to controlprocessor 522. In accordance with the subset of information bits,control processor 522 provides a code channel selection signal to Walshsymbol generator 508 and provides a frequency selection signal tovariable frequency synthesizer 516.

The remaining information bits to be transmitted are provided to CRCgenerator 502, which generates and appends a set of bits that can beused to determine whether the decoded data received at the receiver iscorrect. The bits from CRC generator 502 are provided to encoder 504. Inone embodiment, encoder 504 is a convolutional encoder, though thepresent invention is equally applicable to any error correction encoder.Convolutional encoders are well known in the art.

The encoded symbols are then provided to channelizer 506. Channelizer506 is provided with a time varying spreading sequence fromcorresponding variable sequence generator 508. In one embodiment,variable sequence generators 508 provides sequences in accordance with apredetermined set of orthogonal Walsh sequences. The Walsh sequence datafrom channelizer 506 is provided to scrambler 510 which scrambles thedata in accordance with a pseudorandom sequence provided by PN generator512. Channelizers and sequence generators are well known in the art andare described in detail in the aforementioned U.S. Pat. No. 5,103,459.The scrambled data is provided to mixer 514. Mixer 514 is driven by avariable frequency synthesizer 516. Variable frequency synthesizer 516generates and provides and driving frequency in accordance with afrequency selection signal from control processor 522 which selects thedriving frequency in accordance with a subset of the information bits tobe transmitted. The upconverted data is provided to transmitter (TMTR)518 for transmission through antenna 520.

FIG. 12 illustrates a receiver designed to receive spread spectrum datawhich changes frequency and code channel in accordance with a subset ofthe transmitted data.

Referring to FIG. 12, the transmitted signal is received by antenna 600and provided to receiver (RCVR) 601. Receiver 601 filters and amplifiesthe signal and provides the received signal to a bank of downconverters602 a-602 i. Each downconverter 602 a-602 i is driven by a correspondinglocal oscillator 604 a-604 i.

Each downconverted signal is provided to a corresponding descrambler 606a-606 i. Descramblers 606 a-606 i unscramble the down-converted signalin accordance with a pseudorandom sequence provided by a correspondingPN generator 608 a-608 i. The descrambled sequences from descrambler 606a are provided to dechannelizers 610 a-610 j and the descrambledsequences from descrambler 606 i are provided to dechannelizers 610k-610 n which dechannelizes each descrambled sequence according to allsequences. Each dechannelizers 610 a-610 n is driven by a correspondingsequence generator 612 a-612 n. In one embodiment, sequence generators612 a-612 n are orthogonal Walsh sequence generators. The despread datais provided to decoders 614 a-614 n which decodes the data based on thetype of encoder used by the transmission system. In one embodiment, theencoder is a convolutional encoder and decoders 614 a-614 n are trellisdecoders. The decoded data is provided to CRC check element 616 a-616 nwhich determines whether the decoded check bits correspond to thedecoded information bits.

For each decoded stream of data and a set of quality metrics for eachstream of data is provided to control processor 618. Control processor618 selects the frame with the best quality to be output to the user, asdetermined by the values of the metrics. If all of the decoded frameshave inadequate quality then an erasure is declared. Examples of qualitymetrics which can be used by control processor 618 to select the frame,include: (1) accumulated branch metrics from trellis decoders 612 a-612n, (2) symbol error rate (SER), and (3) CRC check results.

The previous description of the preferred embodiments is provided toenable any person skilled in the art to make or use the presentinvention. However, various modifications to these embodiments will bereadily apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other embodiments without the need forfurther invention. Thus, the present invention is not intended to belimited to the embodiments shown herein, but rather is to be accordedthe widest scope consistent with the principles and features recited inthe claims which follow.

1. A method comprising: modulating data; scrambling a subset ofinformation bits of the modulated data; selecting a frequency inaccordance with the modulated, scrambled subset of information bits; andupconverting the modulated data using the selected frequency.
 2. Themethod of claim 1, further comprising: scrambling another subset ofinformation bits of the data; and selecting a code channel in accordancewith the another subset of information bits, wherein the data ismodulated using the selected code channel.
 3. The method of claim 1,further comprising generating a selection signal in accordance with themodulated, scrambled subset of information bits, wherein the frequencyis selected in accordance with the selection signal.
 4. The method ofclaim 1, wherein the frequency is selected in accordance with apseudorandom sequence.
 5. The method of claim 1, wherein theupconverting the modulated data comprises using a variable frequencysynthesizer to generate the selected frequency.
 6. The method of claim1, wherein the data is modulated using a Walsh code.
 7. The method ofclaim 2, wherein the code channel is selected in accordance with apseudorandom sequence.
 8. The method of claim 5, wherein the variablefrequency synthesizer comprises a direct digital synthesizer.
 9. Anapparatus, comprising: means for modulating data to be transmitted;means for scrambling a subset of information bits of the modulated data;means for selecting a frequency in accordance with the scrambled subsetof information bits; and means for upconverting the modulated data usingthe selected frequency.
 10. The apparatus of claim 9, further comprisingmeans for selecting a code channel to modulate the data, wherein thedata is modulated using the selected code channel.
 11. The apparatus ofclaim 9, further comprising: means for scrambling another subset ofinformation bits of the data; and means for selecting a code channel inaccordance with the another subset of information bits, wherein the datais modulated using the selected code channel.
 12. The apparatus of claim9, further comprising means for generating a selection signal inaccordance with the modulated, scrambled subset of information bits,wherein the frequency is selected in accordance with the selectionsignal.
 13. The apparatus of claim 9, wherein the frequency is selectedin accordance with a pseudorandom sequence.
 14. The apparatus of claim9, wherein the means for upconverting the modulated data comprises usinga means for variable frequency synthesizing to generate the selectedfrequency.
 15. The apparatus of claim 9, wherein the data is modulatedusing a Walsh code.
 16. The apparatus of claim 11, wherein the codechannel is selected in accordance with a pseudorandom sequence.
 17. Theapparatus of claim 14, wherein the means for variable frequencysynthesizing comprises a direct digital synthesizer.
 18. A computerprogram product, comprising: computer-readable medium comprising: codefor causing a computer to: modulate the data; scramble a subset ofinformation bits of the modulated data; select a frequency in accordancewith the scrambled subset of information bits; and upconvert themodulated data using the selected frequency.
 19. The computer programproduct of claim 18, said code further comprising: scrambling anothersubset of information bits of the data; and selecting a code channel inaccordance with the another subset of information bits, wherein the datais modulated using the selected code channel.
 20. The computer programproduct of claim 18, said code further comprising generating a selectionsignal in accordance with the modulated, scrambled subset of informationbits, wherein the frequency is selected in accordance with the selectionsignal.
 21. The computer program product of claim 18, wherein thefrequency is selected in accordance with a pseudorandom sequence. 22.The computer program product of claim 18, wherein the upconverting themodulated data comprises using a variable frequency synthesizer togenerate the selected frequency.
 23. The computer program product ofclaim 18, wherein the data is modulated using a Walsh code.
 24. Thecomputer program product of claim 19, wherein the code channel isselected in accordance with a pseudorandom sequence.
 25. The computerprogram product of claim 22, wherein the variable frequency synthesizercomprises a direct digital synthesizer.
 26. An apparatus comprising: amodulator adapted to modulate data; a scrambler adapted to scramble asubset of information bits of the modulated data; a switch adapted toselect a frequency in accordance with the modulated, scrambled subset ofinformation bits; and an upconverter adapted to upconvert the modulateddata using the selected frequency.
 27. The apparatus of claim 26,further comprising: a processor further adapted to select a code channelin accordance with the another subset of information bits, wherein thedata is modulated using the selected code channel and wherein saidscrambler is adapted to scramble another subset of information bits ofthe data.
 28. The apparatus of claim 26, further comprising a processorto generate a selection signal in accordance with the modulated,scrambled subset of information bits, wherein the frequency is selectedin accordance with the selection signal.
 29. The apparatus of claim 26,wherein the frequency is selected in accordance with a pseudorandomsequence.
 30. The apparatus of claim 26, wherein the upconverting themodulated data comprises using a variable frequency synthesizer togenerate the selected frequency.
 31. The apparatus of claim 26, whereinthe data is modulated using a Walsh code.
 32. The apparatus of claim 27,wherein the selection signal is generated in accordance with apseudorandom sequence.
 33. The apparatus of claim 30, wherein thevariable frequency synthesizer comprises a direct digital synthesizer.